Vulkan: Fix xfb query ASSERT on end It's possible for the xfb query to have never been issued, as it's deferred until a draw call with xfb active is encountered, which may never happen. Bug: chromium:1209285 Change-Id: I893f9f9a06e4b9f2f9da9406affab0be3598fcb4 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3294701 Reviewed-by: Tim Van Patten <timvp@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>